This invention relates generally to oil injection systems for two-stroke internal combustion engines, and more particularly to an oil detector adapted to set off an alarm should the oil supply fall below a safe operating level.
The two-stroke internal combustion engine undergoes two piston strokes or only one revolution for each cycle of operation. Exhaust ports in the cylinder wall are uncovered by the piston near the end of the expansion stroke to permit the escape of exhaust gases and reduce the pressure in the cylinder. The fuel charge flows into and is compressed in a separate crankcase compartment. Intake ports are uncovered by the piston soon after the opening of the exhaust, and the compressed charge flows into the cylinder, expelling most of the exhaust products.
In a crankcase-scavenged, two-stroke engine, the crankcase is hermetically sealed so that it can function as a pump in conjunction with the piston. In less expensive forms of crankcase-scavenged engines, the lubricating oil is mixed with the gasoline. The ratio of oil to gasoline in the mixture is determined by taking into account the oil requirements of the engine at maximum operating speed.
The difficulty with using a predetermined oil-to-gas ratio is that at low and medium operating speeds, the relative amount of oil is in excess of engine requirements, as a consequence of which oil is wasted and harmful deposits build up in the exhaust pipe, the muffler and in the combustion chamber. These deposits usually give rise to pre-ignition and a decrease in compression as well as irregular combustion and poor cooling efficiency.
To obviate this difficulty, it is now the practice in some two-stroke engines, as for example in motorcycles, such as the Suzuki TS-400L and the Kawasaki H-2 750, to segregate the gasoline supply from the oil supply. In such arrangements, oil from the oiltank is gravity fed through an oil line to an oil pump which functions to inject the oil into the crankcase under pressure. The ratio of oil to gasoline is automatically adjusted as a function of the throttle opening so that this ratio varies in accordance with engine speed and the amount of oil is never in excess of engine requirements. As a consequence, engine performance is markedly improved.
In a two-stroke engine in which the oil is pre-mixed with the gasoline, should the fuel mixture become exhausted, the engine will merely cease to function, but the engine will in no way be damaged by the absence of the mixture. However, in an engine in which the oil is separately injected, when oil is depleted, the engine continues to be supplied with gasoline and keeps running. As a consequence, the piston may seize and the engine structure may be otherwise impaired due to the dearth of lubrication. On existing types of two-stroke engines, no means are provided to indicate the depletion of oil.